The inlet flue systems of most conventional electrostatic precipitators have many horizontal or nearly horizontal lower surfaces onto which particulates in the gases flowing to the precipitator chambers settle and accumulate. Often, the weight of the accumulated particulates builds to a level several times that of the flues themselves and requires the flues and the structures supporting them to be strong and heavy, and correspondingly costly. The settled particulates increasingly disrupt normal gas distribution by changing, usually unpredictably, the internal shapes and dimensions of the flow passages in the flues and between turning vanes. Some flow passages may even become plugged.
The tons and tons of accumulated particulates must be removed periodically. Often, removal can be accomplished only by manual shovelling, which is costly and time consuming and requires extended shutdown of an entire plant.
It is common practice in designing precipitator inlet flue systems to maintain relatively high gas flow velocities (about 50 feet per second) in order to minimize particulate settling. Reducing the gas flow from conveying velocity to precipitation velocity complicates the structures of transition sections to provide reasonably uniform distribution at the entrance to each precipitator chamber and generally involves providing multiple stages of perforated plates with attendant draft losses.